3 1/2â€³ x 6â€³ Variable Rams.
24 November 2012
For some reason we seem to be going through these rams at regular intervals, Has anyone has similar problems, as regards the above. They seem to have a very short life span in the BOP. 15 to 20 closures.
Everything hinges around the unsuported/exposed area of the variable bore rams.
Every time we stepped out of the middle of the road 5" x 3.5" we had mishaps. All reports qualify the rams as tricky and/or erratic.
There are the Exxon tests of 15,000 psi Working Pressure BOP back in 1984, and Vendors Product Alerts and Engineering Bulletins covering sizes, rubber compounds, temperature limits ,hang-off weight limitations worth consulting.
I would try hard to have the span reduced even at the expense of two VBR - one say 3.5" to 4.5" other to 5" x 6" for instances.
The flex packer was one of the solutions to overcome some of the weaknesses of a particular combination of VBRs. (See publication OTC 7336 on High Temperature VBRs)
Need some more info. If you don't want to specifically name the make and model of BOP, that's OK.
But are they:
surface or SS?
18Â¾" or 13â…" or ...?
5K or 15K? And what test pressures are you using?
Are the closures routine function and pressure testing, or are they being used in anger?
What size of pipe are you closing them on?
Are you hanging off on the VBR's?
Are you having to strip through them?
What operating pressure are you using when you function them?
Are the rubber goods OEM?
I guess that the VBR's are failing to test, but what do the rubber goods look like when you strip them apart?
Which parts of the rubber goods fail (upper seal, front packer etc)?
I am guessing that your BOP will be a more recent model. It could be a manufacturing issue of the ruber goods.
Search the website for a question about annular packer life - most of the comments there will apply to this problem.